The technique of MIMO transmission (or spatially multiplexing) is a technique for increasing the spectral efficiency of a communication link, by enabling multiple streams to be sent at the same time and frequency. MIMO transmission can be categorized into two different techniques: single user MIMO (SU-MIMO) and multi-user (MU-MIMO). SU-MIMO supports only one user and can only maintain one communication link at one time. MU-MIMO however can support multiple users and therefore can support several links at the same time.
There are potential capacity benefits for MU-MIMO in any system in which one communication entity communicates with more than one other communication entity at the same time. Examples of such systems include cellular mobile communications and indoor WLAN (wireless local area networks) systems. Presently MU-MIMO is used in a number of different communication systems in conjunction with digital beam forming. Examples of such systems are IEEE 802.11ac [1] and the LTE standard. (Extensive support for which is provided from release 10 [2] onwards.)